In the news today: Conservationists are working hard to prevent 150 long-finned pilot whales, Globicephala melas, from stranding in Loch Carnan (South Uist, Outer Hebrides).
The pod was discovered yesterday and members of the British Divers Marine Life Rescue (BDMLR) and the Scottish Society for the Prevention of Cruelty to Animals SSPCA) are working hard to coerce the animals back into deeper waters. The main concern is that the 20 or so injured individuals will attempt to strand themselves and due to their strong social bonds the remaining individuals will follow their conspecifics, which will result in the largest mass stranding event that Scotland has ever seen.
This is not the first time that long-finned pilot whales have been found at risk of stranding in Loch Carnan. In October 2010 the BDMLR and the SSPCA were involved with the prevention of a mass stranding of around 30 individual long-finned pilot whales. Unfortunately, a week later, on the 6th November, the Irish Whale and Dolphin Group (IWDG 2010) confirmed the death of 33 beached long-finned pilot whales. It is thought that these stranded individuals were the same individuals that were under observation in Loch Carnan.
In the same month, 16 short-finned pilot whales (Globicephala macrorhynchus), found predominantly in warmer waters, were found stranded in Cudjoe Key, Lower Florida Keys on Thursday 5th May. The Florida Fish and Wildlife Conservation Commission in conjunction with other organisations managed to successfully refloat 7 individuals. In 2003, 28 short-finned pilot whales mass stranded in the same location in the Florida Keys.
In the same year, 107 pilot whales, thought to be long-finned pilot whales due to their distribution in colder, temperate waters, were found stranded near Cavalier Creek on Stewart Island, New Zealand on the 20th February. Around half of the whales were still alive when members of the Department of Conservation arrived at the scene but due to their high position upon the beach and the length of time that they had been stranded for, it was in the best interest of the animal’s welfare to euthanize those individuals.
Pilot whales (Globicephala sp.) belong to the Odontocetes, toothed whales, and grow to between 4 and 6 m in length. They are black in colour with a bulbous head and are known to feed predominantly on squid species found down to depths of 150 m (Beatson et al. 2007). Adult male long-finned pilot whales are capable of diving to greater depths, such as 600 m, in search of food as they are larger-bodied (Baird et al. 2002). As with other odontocetes, pilot whales use echolocation to locate their prey and map out the underwater environment and this is potentially one cause of these mass stranding events.
Any source of loud noises underwater would disorientate the animals causing them to panic and rush to the surface which could lead to decompression sickness or the bends. With the mass stranding in New Zealand occurring only days before the major earthquake that hit Christchurch it is possible that seismic activity caused the mass stranding. The controversial issue of navy sonar and oil and gas exploration being used in areas of inhabited by pilot whales is another source of deafening noise that would startle the animals.
Since pilot whales are migratory animals simple disorientation, for example within the fjords of New Zealand is another potential cause of the strandings. Parasites and disease have also been shown to cause mass strandings, for example Morimitsu et al. (1987) found parasites in the eight cranial nerve (linked to the ears) of stranded pilot whales. Due to their loyal social structure, healthy individuals will follow sick pod members into shallow waters and become stranded themselves. Pilot whales, like many other toothed whales, have a stable matrilineal structure with related females and their juveniles forming a pod (Amos et al. 1991). This highly related composition of individuals is the source of their loyalty and in the observed cases their demise.
by Rachel Lambert, Sea Watch Foundation
Amos, B., Barrett, J. & Dover, G.A. (1991) Breeding behaviour of pilot whales revealed by DNA fingerprinting. Heredity 67: 49-55.
Baird, R.W., Fabrizio Borsani, J., Bradley Hanson, M. & Tyack, P.L. (2002) Diving and night-time behaviour of long-finned pilot whales in the Ligurian Sea. Marine Ecological Progress Series. 237: 301-305.
Beatson, E., O’Shea, S. & Ogle, M. (2007) First report on the stomach contents of long-finned pilot whales, Globicephala melas, stranded in New Zealand. New Zealand Journal of Zoology. 34: 51-56.
Morimitsu, T., Nagai, T., Ide, M., Kawano, H., Naichuu, A., Koono, M. & Ishii, A. (1987) Mass stranding of odontoceti caused by parasitogenic eight cranial neuropathy. Journal of Wildlife Diseases. 23(4): 586-590.